An eccentric phase of training is the phase when a tight muscle is stretched under load. By eccentric contraction the muscle-tendon complex stretches and absorbs the mechanical energy. An extensive eccentric training causes a number of muscle adaptations that are advantageous for after-workout recovery and sports events. Muscles can generate a significantly greater eccentric force in comparison with a concentric force. In the eccentric phase, the force is generated by both contractile elements of muscle fibers and by viscoelastic components of connective tissue. At the same time, by concentric contractions the force is generated only by contractile elements.
While performing high intensity eccentric exercises, the muscle mass is increased due to the growth of fiber width and the quantity of sarcomeres, mainly, fibers of the II type. In contrast to the traditional concentric training with weights, hypertrophy happens earlier at the eccentric training. Researchers have found that the muscle stretching in the eccentric phase stimulates muscle protein synthesis better than the concentric contraction does.
High intensity eccentric exercises provide a significant increase in strength that is higher than by concentric exercises. Current scientific data for trained sportsmen show that the eccentric exercises effectively increase the strength. Further, an explosive strength can be increased. Taking into account that the muscular fatigue can be incomplete in the concentric exercises, the usage of eccentric phase can lead to higher fatigue of motor units in the body and thus create an additional stimulus to hypertrophy.
Regular eccentric exercises can increase contractile part of a muscle without visual length increase. As a result, two important changes of a muscle function happen: the speed of contraction increases; the force peak is developed earlier. This enables better protection of joints by muscles against damages which can be caused by quick movements because muscles begin to contract earlier, thus increasing the control over a movement. It is one of the reasons to recommend eccentric exercises for prevention of injuries and for rehabilitation.
Eccentric exercises also require much lower level of oxygen consumption and stress on the cardiovascular system as well as lower level of perceived load for any level of the complexity of exercises. Therefore, it was proved that eccentric exercises were the perfect choice for elderly people and people suffering from cardiovascular collapse as the eccentric exercises help to build up muscles quickly and safely, and significantly decrease injury risks without overloading the cardiovascular system.
There exists still a need for improving efficiency of weight training and for providing an exercise machine for this.